If I click my mouse into a pinned-open cell source text box (or in safe mode, into any cell source) which is not already entirely in view, the page re-scrolls to fit as much of that box as possible onto the screen.
(Even more annoying, about half the time I end up getting a text selection between whatever point in the box was under my mouse pointer when I clicked and whatever point ends up under my mouse pointer after the re-scroll.)
Re-scrolling may be helpful when a box is navigated into via keyboard, but as part of mouse interaction it is very disorienting, and should be avoided.
I guess you’re talking about jumpy behavior that I sometimes notice when editing a notebook. I’ve never been able to pin down what caused that but I guess you’re right - it’s intended to re-scroll to the clicked cell.